Emissions from fossil fuel combustion facilities, such as flue gases of coal-fired utilities and municipal solid waste incinerators, typically include mercury. The emissions include vaporized mercury as elemental mercury, Hg0, and/or as part of mercury-containing compounds (e.g., an oxidized form of mercury (Hg+2), such as in mercuric chloride or mercuric nitrate).
Many countries regulate emissions of mercury within waste gases because of potential environmental hazards posed by the mercury emissions. Hence, facilities generating gas emissions that can contain mercury typically utilize a mercury monitoring system to measure total mercury concentration in the emissions to comply with the regulations. Certain mercury monitoring systems include a converter that converts the oxidized mercury within the emissions into elemental mercury, such as by using a mercury converter performing a thermal conversion or cracking process. The mercury monitoring systems then measure the total amount or concentration of elemental mercury within the emissions using an analyzer, such as an atomic fluorescence spectrometer.
To ensure accurate measurement of the elemental mercury concentration within the emissions, the mercury monitoring systems typically include a calibration assembly. A conventional calibration assembly provides vaporized elemental mercury to the analyzer at a particular concentration. The analyzer compares the amount of elemental mercury with that of dry, substantially mercury-free gas, such as provided by a dilution gas supply. The results of the comparison allow an operator to calibrate the mercury monitoring system.